[P-PS09] 火星と火星衛星

[PPS09-P14] Seasonal Variations of Hydrated Sulfates in Martian Polar Dunes: Insights from White Sands Analog Studies

*千々岩 拓夢¹、長谷川 精²、ルジ トリシット¹、小松 吾郎⁴、庄崎 弘基⁵、菊池 早希子⁶、佐久間 杏樹³、臼井 寛裕⁷ (1.岡山大学大学院環境生命自然科学研究科、2.高知大学、3.東京大学、4.ダヌンツィオ大学、5.東京科学大学, ELSI、6.JAMSTEC、7.JAXA)

キーワード：火星、石膏砂丘、高緯度地域、ホワイトサンズ、地球アナログ、宇宙生物学

Understanding the mineralogical composition of Martian sulfate deposits is crucial for reconstructing past aqueous environments and assessing the planet’s habitability. Spectroscopic studies have demonstrated the presence of various types of hydrated minerals in sediments around the north polar cap of Mars. Previous research has shown that liquid salt water may exist at high latitudes on Mars, suggesting the possibility of transient briny water activity in these regions. Specifically, gypsum, a hydrated calcium sulfate (CaSO₄+2H₂O), has been detected around Olympia Planitia, where sand dune fields are distributed (Langevin et al., 2005b). To further define the geographic distribution and formation and accumulation process of these hydrated minerals, we conducted a field survey at White Sands, New Mexico, USA, on Earth, where gypsum sand dunes have developed similarly to Mars. White Sands serves as an excellent terrestrial analog for Martian gypsum dunes due to its similar geomorphological setting and evaporite-driven sedimentation processes (Ghrefat et al. 2011, Baitis et al. 2014). At White Sands, salt precipitates when Lake Lucero evaporates during the dry season, and is then transported by wind to form sand dunes. XRD analysis of samples from the evaporation site of Lake Lucero detected bassanite (CaSO₄+1/2 H₂O). Because bassanite has a higher solubility than gypsum, it is possible that bassanite precipitated when the salt lake evaporated and the salt concentration increased. This transformation process suggests that metastable phases such as bassanite could form under specific evaporation conditions, providing a plausible pathway for their presence in Martian dunes.
Based on this knowledge, in this study, we further analyzed the seasonal variation of mineral composition in the sand dune fields around the north polar cap of Mars using remote sensing data. These results suggest that both gypsum and bassanite may undergo seasonal variations on Mars, possibly linked to transient briny water activity. However, further analysis is necessary to confirm the mechanisms driving these mineralogical changes.